Calender and method for controlling such a calender

ABSTRACT

A calender includes a rotatable roller, and a belt, co-acting with the roller with a determined belt pressure. At least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender. The calender also includes heating means for heating the fluid and/or the roller, control means for controlling the heating means and/or the belt pressure and/or the contact time, and flow influencing means for initiating and/or influencing a flow of the fluid in the internal space. The control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner. A set with a plurality of such calenders and a method for controlling such a calender.

The invention relates to a calender, comprising:

-   -   a rotatable roller, which roller is hollow and thereby defines         an internal space which can be filled at least partially or is         filled at least partially with a heatable fluid, such as oil or         air;     -   a belt, co-acting with the roller, with a determined belt         pressure, wherein a material for feeding through the calender is         situated between the roller and the belt for a determined         contact time during throughfeed through the calender;     -   heating means for heating the fluid and/or the roller, which         heating means are optionally disposed in the internal space; and     -   one or more control means for controlling the heating means         and/or the belt pressure and/or the contact time.

Such a calender is per se known. Particularly known are different types of calender. There is thus for instance a type of calender which is used for throughfeed of a material, wherein a print is fixated on the material if the material already had a print printed thereon prior to throughfeed through the calender, or is transferred thereto from a so-called transfer paper if the material did not yet have a print prior to throughfeed through the calender. Such a calender can also be referred to as a device for transfer and/or fixation. Another type of calender is a laminating calender or laminating device, wherein multiple materials are fed through the calender and are here bonded to each other, i.e. laminated. The material or the materials can be any desired and/or suitable material, such as for instance textile.

The calendering process takes place under the influence of heat. The heat comes from the heating means which heat the fluid, such as oil or air, whereby the roller is heated by the heated fluid, and optionally in that the heating means heat the roller directly, for instance by radiation. Direct heating of the roller by for instance radiation takes place particularly in the case of air-filled rollers. Indirect heating by the heating means via the heatable fluid takes place particularly in the case of both oil-filled and air-filled rollers. The heating can be set as desired, particularly by controlling the heating means in desired manner Controlling the heating means can for instance comprise of controlling a power of the heating means.

The calendering process further takes place under the influence of pressure. The pressure is provided by said belt and can be set as desired, particularly by controlling the belt pressure in suitable manner, more particularly by tightening the belt or arranging the belt more loosely, whereby the pressure is respectively increased and reduced.

In addition to the heat and pressure, the contact time, i.e. the amount of time that the at least one material is in direct or indirect contact with the roller, can also be particularly important for the calendering process. The contact time can be set as desired, for instance by selecting a rotation speed of the roller. Controlling of the contact time can therefore alternatively or additionally be formulated as controlling of the roller, more particularly controlling of the rotation speed of the roller, still more particularly controlling of drive means for rotating driving of the roller.

For the sake of simplicity the one or more control means are also referred to below as “the control means”.

The control means control the heating means and/or the belt pressure and/or the contact time such that a desired calendering process should be achieved. It has however been found by applicant that, despite this control, the result of the calendering process is not always fully as desired and/or consistent. It is an object of the invention to at least reduce or preferably obviate this drawback.

This object can be achieved by means of a calender according to claim 1.

According to the invention, flow influencing means are provided which make it possible to initiate a flow of the fluid in the internal space or, to the extent that there already is such a flow, influence it. Also provided are control means for controlling the flow influencing means and thereby the flow of the fluid in the internal space, wherein the control means are configured to control the flow influencing means in freely settable manner. The control means can be the same control means as the one or more control means which are configured to control the heating means and/or the belt pressure and/or the contact time, or further control means which are additionally provided. For the sake of simplicity, reference will be made below of “the control means” for controlling of the flow influencing means and/or heating means and/or the belt pressure and/or the contact time, which can thus be understood to mean both the same control means and different control means. It is noted that, if desired, “the control means” could alternatively be referred to as “the one or more control means” for the heating means and/or the belt pressure and/or the contact time and as “the optional further control means” for the flow influencing means.

It has been found by applicant that there can be a relatively great difference between a temperature of the fluid and an (outer periphery) temperature of the roller. Such a temperature difference can for instance lie between 10° C. and 30° C., depending on the type of calender used. It has further been found by applicant that a heat transfer between the fluid and the roller can be influenced by influencing the flow of the fluid in the internal space, whereby the temperature difference between the fluid and the roller can be influenced. The heat transfer between the fluid and the roller can for instance be increased, whereby the difference in temperature between the fluid and the roller can be reduced. The heat transfer between the fluid and the roller can for instance be reduced, whereby the difference in temperature between the fluid and the roller can be increased. It has been found by applicant that by also aiming for a flow of the fluid in addition to controlling the heating means and/or the belt pressure and/or the contact time, a good and/or accurate calendering process can be provided.

It has further been found by applicant that, particularly in the case of an oil-filled roller, influencing the flow of the fluid with the flow influencing means can take place more quickly than influencing a temperature of the fluid with the heating means. According to the invention, an (outer periphery) temperature of the roller can therefore be adjusted relatively quickly, at least in the case of oil-filled rollers, by adjusting the flow of the fluid. Because the (outer periphery) temperature of the roller can be adjusted relatively quickly according to the invention, variations in the print on the substrate can be reduced or preferably even prevented.

It has further been found by applicant that, particularly in the case of an air-filled roller, a more homogenous heating with air can take place by using the flow influencing means.

It is noted that the degree of heat transfer from the fluid to the roller can for instance be determined by temperature differences in the fluid, such as gradients in the fluid. When the temperature differences in the fluid are small, particularly in the case of a small temperature gradient in the direction of the roller, a heat transfer from the fluid to the roller can be relatively great. When the temperature differences in the fluid are great, particularly in the case of a large temperature gradient in the direction of the roller, a heat transfer from the fluid to the roller can be relatively small. By adjusting the flow of the fluid temperature differences in the fluid, particularly a temperature gradient in the direction of the roller, can be adjusted, particularly increased or reduced, and with this the heat transfer to the roller.

It is further noted that freely settable can at least be understood to mean that the setting of the flow influencing means is independent or separate from the setting of another component, such as for instance the roller, more particularly the rotation of the roller. Freely settable can alternatively or additionally be understood to mean that the flow influencing means can be set not just to two values, such as on or off, but to at least a plurality of values. The setting can take place in stepped manner or continuously.

It is further noted that the flow influencing means are preferably provided in addition to and/or separately of the roller so that they are freely settable at least relative to the roller.

The heating means can be disposed outside the internal space of the roller, but can alternatively also be disposed in the internal space. Disposing or placing in the internal space makes the calender more compact, and further makes it possible to heat the fluid in the vicinity of the peripheral wall of the roller and/or to heat the roller directly, so that a relatively rapid heating of the roller can take place. In an embodiment the heating means can be embodied as electrical heating element, such as for instance a glowing or radiating heating element.

The fluid can be any suitable fluid but is preferably oil or air. It is preferably contained in a system which is closed at least to said fluid and comprises at least the internal space of the roller, and optionally for instance an expansion tank connected via at least one conduit to the internal space. And oil, such as particularly thermal oil, for instance mineral thermal oil or synthetic thermal oil, has a heat transfer coefficient suitable for the invention and can moreover be heatable to a relatively high temperature without this greatly reducing the lifespan. Oil can alternatively or additionally have a large heat capacity. Air has the great advantage that it keeps the calender relatively simple and is able to increase or reduce the temperature of the roller relatively quickly.

The roller will typically be a cylindrical body. During operation this body will generally be rotated about its rotation axis, in practical manner its width axis, at a desired rotation speed by means of drive means, wherein the substrate is carried over the outer periphery.

The control means are preferably embodied as an electronic device with at least one input and one output and a processor, such as a microprocessor, which device controls the at least one output on the basis of the information at the at least one input, for instance a programmable logic controller (PLC).

Although calendering processes, such as transfer and/or fixation processes or laminating processes, can be performed in continuous operation, a batch process will however occur in most cases, including a start-up phase at the start of the batch process and a shutdown phase at the end of the batch process.

As elucidate above, the control means can preferably be configured to set the flow influencing means on the basis of a desired heat transfer between the fluid and the roller. This can be achieved in diverse ways, alone or in any random combination. These ways will be elucidated below on the basis of different embodiments of the device according to the invention.

In the device according to the invention the control means are configured to control the flow influencing means such that a flow speed of the fluid can be set.

The speed of the flow can at least partially determine the heat transfer between the fluid and the roller. Because the control means can in this embodiment control the flow influencing means such that this speed can be adjusted, the option exists of adjusting the heat transfer between the fluid and the roller.

Setting can here be understood to mean at least that the flow speed of the fluid can be adjusted or varied.

The flow speed of the fluid can particularly be set between 0, i.e. stationary, and V_(max), wherein V_(max) can for instance lie between 3 and 15 m/s, for instance depending on the fluid. The higher the speed, the higher a heat transfer to the roller can be and/or the more homogenous the temperature of the fluid can be.

In an embodiment of the device according to the invention the control means are configured to control the flow influencing means such that a direction of the flow of the fluid is substantially opposite to a rotation direction of the roller.

A flow of the fluid in a direction substantially opposite to the rotation direction of the roller provides a relatively high heat transfer between the fluid and the roller, i.e. a relatively small temperature difference between the fluid and the (outer periphery of the) roller. By setting the direction of the flow as being opposite to the rotation direction of the roller, the heat transfer between the fluid and the roller, among other things, can be set hereby. The opposite direction can here particularly be a tangential direction.

It is noted that setting of the direction of the flow can be achieved in different ways. Several practical embodiments will be elucidated below on the basis of exemplary embodiments of the device according to the invention.

The flow speed of the fluid can here be higher than, lower than or equal to the rotation speed of the roller, wherein the absolute value of the flow speed must be considered. If a higher heat transfer between the fluid and the roller is desired and the flow influencing means are set to make the fluid flow in the opposite direction, a fluid speed which is higher relative to the rotation speed of the roller can preferably be opted for here.

In another embodiment of the device according to the invention the control means are configured to control the flow influencing means such that the flow regime of the fluid can vary between turbulent and laminar.

A turbulent flow of the fluid can provide a higher heat transfer between the fluid and the roller relative to a laminar flow. Depending on a desired degree of heat transfer between the fluid and the roller, the flow influencing means can be set such that the flow is turbulent or laminar.

As known to the skilled person, the transition from turbulent to laminar is determined on the basis of the Reynolds number Re and the geometry of the internal space.

Varying is here understood to mean that the flow regime in the fluid can be both turbulent and laminar, and generally does not mean that it switches continuously between the two.

The flow influencing means can be embodied in diverse ways.

The flow influencing means for instance comprise a rotatable rotor with a number of blades which is optionally disposed in the roller.

A rotor rotates about its rotation axis and has a relatively simple construction and/or is relatively inexpensive, and can influence or at least initiate the flow in the fluid in simple manner. The rotor can thus be rotatably driven at a desired rotation speed so as to set a flow speed of the fluid and/or the rotor can be rotatably driven in a direction opposite to the rotor so as to make a flow direction of the fluid opposite to the rotation direction of the roller.

The rotor is preferably disposed in the roller, more particularly in the internal space in the roller, because influencing of the flow can thereby be performed well and/or relatively quickly. The placement of the flow influencing means in the internal space can moreover mean that less fluid is necessary to completely fill the internal space, whereby a maximum power of the heating means can be lower and/or the heating means will be able to achieve a heating of the fluid to a determined temperature more quickly.

In another embodiment of the device according to the invention device comprises first drive means for rotatably driving the roller and second drive means for rotatably driving the rotor, and the control means are configured to control the first and second drive means separately of each other.

It is advantageous for first drive means for the roller to be provided, which are separate or disconnected from second drive means for the rotor. This makes it possible to set each of the roller and the rotor to its own rotation speed (with a determined rotation direction), independent of the other of the roller and the rotor, which can be deemed favourable subject to the process conditions in a calendering process. The control of the first drive means runs via said one or more control means or via optionally further provided control means.

It is particularly advantageous here for the control means to be configured to control the first and second drive means such that the rotor rotates in a direction opposite to the roller and/or rotates at a relatively high speed when the outer periphery temperature of the roller is lower than a desired temperature of the outer periphery of the roller.

In combination therewith or as an alternative thereto, it is preferred that the control means are configured during the start-up phase and/or shutdown phase of a calendering process to control the first and second drive means such that the rotor is rotated in a direction opposite to the roller. During both starting up and shutting down of a calendering process, such as a transfer and/or fixation process, this has the result that the outer periphery of the roller is brought to temperature relatively quickly (start-up phase) or that the heating means can be switched off or can be set to a lower power sooner (shutdown phase).

The rotor can preferably be driven by the second drive means between a minimum rotation speed equal to 0 revolutions/s and a maximum rotation speed V_(rotor,max), which maximum rotation speed can depend, among other factors, on the fluid and/or a diameter of the rotor, and which amounts to for instance 2 revolutions/s, wherein V_(rotor,max) is opposite to the rotation direction of the roller.

In another embodiment of the device according to the invention the rotor comprises a cylindrical body disposed in the internal space of the roller, wherein the fluid is situated between the rotor and the roller, at least during use of the calender, wherein the blades extend outward from the cylindrical body, substantially in the direction of the roller.

Such a rotor can be suitable for appropriately influencing the flow of the fluid.

When the rotor is embodied in this way, the volume that is filled with fluid is reduced to an annular space between the cylindrical rotor and the peripheral wall of the roller, whereby relatively little fluid is necessary in comparison.

The body can here be completely solid but also hollow, wherein a hollow mass has the advantage that this reduces the mass of the rotor, whereby it can be rotated more easily and whereby the total mass of the device is also smaller.

It has been found by applicant that the rotation speed of the roller and the rotation speed of the rotor can be related. It can therefore be advantageous for the flow influencing means to also be controlled on the basis of a number of revolutions of the roller. The number of revolutions of the rotor can thus for instance also be reduced when a number of revolutions of the roller is reduced, and vice versa.

In another embodiment of the device according to the invention the flow influencing means comprise at least one fluid conduit extending into the internal space and having at least one opening for the purpose of supplying fluid from the at least one fluid conduit via the at least one opening to the internal space of the roller, and comprising at least one fluid discharge for discharging fluid from the internal space.

By providing the fluid conduit fluid can be supplied to the internal space and discharged again via the discharge. Giving the fluid conduit and/or the opening a suitable form and/or selecting a suitable pressure and/or speed of the fluid inflow enables the flow of the fluid to be influenced in desired manner.

It is thus for instance possible to set the inflow direction of the fluid into the internal space, and thereby set a flow direction of the fluid in the internal space, by suitable selection of the at least one opening and/or by providing orienting means, such as flaps or the like, which co-act with the opening. The opening can thus be formed as a tangential opening which supplies the fluid in a direction opposite to the rotation direction of the roller, or orienting means such as a flap can be provided which orient the flow of the fluid in a direction opposite to the rotation direction of the roller when flowing out through the opening. By selecting a speed and/or pressure at which the fluid is supplied, a speed of the fluid flow can be set.

The at least one fluid conduit and the at least one fluid discharge can be connected to each other, optionally outside the roller, in order to feed fluid discharged via the fluid discharge from the roller back to the roller via the at least one fluid conduit.

At least one pump can be provided for the purpose of extracting fluid via the fluid discharge and/or for the purpose of supplying fluid via the at least one fluid conduit and the at least one opening to the internal space of the roller.

The at least one fluid conduit preferably extends over the whole width of the roller.

The at least one fluid conduit preferably comprises a plurality of openings which are preferably disposed distributed with equal mutual pitch distance over the width of the fluid conduit.

The at least one fluid discharge is preferably embodied as a fluid discharge conduit extending into the internal space and having at least one opening.

The at least one fluid discharge conduit preferably extends over the whole width of the roller.

The at least one fluid discharge conduit preferably comprises a plurality of openings which are preferably disposed distributed with equal mutual pitch distance over the width of the fluid conduit.

The openings of the fluid conduit and the fluid discharge conduit can be disposed at the same or different width positions.

Two fluid conduits and two fluid discharge conduits are preferably provided, with an angular distance of 180° between the two fluid conduits and between the two fluid discharge conduits, and with an angular distance of 90° between a fluid conduit and an adjacent fluid discharge conduit.

In another embodiment of the device according to the invention the device comprises at least one first temperature sensor for measuring the temperature of an outer periphery of the roller, wherein the control means are configured to control the flow influencing means and/or the heating means on the basis of the measured outer periphery temperature.

It has been found by applicant that the temperature of the outer periphery of the roller determines to a large extent the calendering process. It is therefore opted for according to the invention to measure the temperature of the roller at the position which substantially determines the process, i.e. at the outer periphery of the roller. Provided for this purpose is at least one first temperature sensor, also referred to below as the first temperature sensor, which measures the temperature at the outer periphery of the roller, i.e. at the external surface of the roller, more specifically at a position where the material comes into contact with the roller and/or in or close to the centre of the roller and/or in the area lying at a distance of at least 20 centimetres from the edges of the roller. When only one first temperature sensor is provided, it is preferably arranged in or close to the centre of the roller.

It has further been found by applicant that a determined, measured outer periphery temperature of the roller can require determined settings and/or adjustments in the control of the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time which result in a good and/or consistent calendering process. The one or more control means according to the invention are therefore configured to control the flow influencing means and/or heating means and/or the belt pressure and/or the contact time on the basis of the measured outer periphery temperature.

In another embodiment of the device according to the invention the device comprises at least one second temperature sensor for measuring the temperature of the fluid, wherein the control means are further configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the measured fluid temperature.

Alternatively to but preferably additionally to the at least one first temperature sensor, the calender can be provided with at least one second temperature sensor (also referred to below as the second temperature sensor) which measures the temperature of the fluid. By controlling on the basis of both the outer periphery temperature of the roller and the fluid temperature the calendering process can be performed well and/or consistently and/or accurately.

In another embodiment of the device according to the invention the at least one first temperature sensor comprises a thermocouple arranged against the outer periphery of the roller.

By arranging a thermocouple against the outer periphery of the roller a very direct measurement of the outer periphery temperature is achieved, which increases the chances of a reliable operation of the calender in respect of the quality of a calendering process. This thermocouple can be arranged against the outer surface at any suitable position. The thermocouple is preferably disposed against the outer surface at a location such that it is disposed at a position where the fed-through material diverges from the roller. The thermocouple hereby does not influence the calendering process.

In another embodiment of the device according to the invention the at least one first temperature sensor comprises an infrared sensor arranged at a distance from the roller.

It is possible by means of an infrared sensor to measure the outer periphery temperature at a distance, without the need for substantial modifications to the calender itself. This makes this embodiment of the calender simpler in terms of construction. An advantage hereof is that the sensor cannot influence the process itself. This infrared sensor can alternatively or additionally be provided on a thermocouple. The infrared sensor can particularly be used with a roller with a teflon coating.

In another preferred embodiment of the device according to the invention the device comprises a plurality of first temperature sensors which are disposed distributed over the width of the roller for the purpose of measuring the temperature of an outer periphery of the roller distributed over the width of the roller.

When a plurality of first temperature sensors is thus provided, the reliability of the measurement is increased. It is possible here that when the calender is controlled on the basis of these multiple first temperature sensors, each of these sensors is considered independently, or that an optionally weighted average of these measurements is used as starting point. In both cases it is possible for a database which is optionally provided and is further elucidated below to store the data of the plurality of first temperature sensors independently of each other. Defects in a temperature sensor can hereby for instance be detected. Such defects can for instance be caused by dust, and occur particularly in the described temperature sensors which are embodied as thermocouple. When temperature sensors embodied as thermocouple are used, there is therefore preferably at least one further temperature sensor, such as a thermocouple or another type of temperature sensor. If a sensor is deemed defective, it is thus possible not to include the measurements of this sensor in the control of the calender, at least until it is replaced. In such a case it is for instance possible to temporarily control on the basis of historical data from the sensor in question, or it is possible to control only on the basis of the other sensors. The first temperature sensors can here be embodied wholly or partially as in the above described embodiments, or can take a different form.

This advantage is here described particularly with reference to the outer periphery temperature and therefore the first temperature sensor, however, the same effect is also to be expected in the case that use is made of a plurality of second temperature sensors for the purpose of measuring the fluid temperature distributed over the width of the roller.

It is noted that it is possible using the plurality of temperature sensors to determine whether there are any differences in temperature over the width of the roller, which can cause variations in the process.

In another embodiment of the device according to the invention the calender or a system of which the calender forms part comprises a database in which at least one of the following data is stored, optionally periodically:

-   -   a or the measured outer periphery temperature of the roller;     -   a or the measured fluid temperature;     -   the contact time;     -   the belt pressure;     -   a power of the heating means;     -   number of revolutions of the roller since the start of a         calendering process;     -   at least one property of the at least one material being fed         through the calender;     -   at least one property of a transfer paper optionally being fed         through the calender;     -   an ambient temperature;     -   an air humidity;     -   which calender is used;     -   a power of drive means of the calender;     -   at least one property of a belt of the calender,

and the control means are further configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of at least one of the data contained in the database.

It is advantageous for the settings of the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time and/or the measured outer periphery temperature of the roller and/or the fluid temperature to be recorded in a database, particularly for calendering processes in which a good and/or consistent calendering result has been achieved, so that the calender can be controlled on the basis of the data contained in the database. By collecting sufficient data from a plurality of calendering processes with the same or different calenders and recording these data in a database it is possible to determine on the basis of the data contained in the database how the control means should control the flow influencing means and/or heating means and/or the belt pressure and/or the contact time in order to achieve a good and/or consistent calendering result.

The process can become even more accurate when other parameters are also recorded in the database, and wherein the calender can also be controlled on the basis of these other parameters. It has been found by applicant that said parameters can influence the calendering process and that it can thereby be useful to record at least these stated parameters. It will be apparent that other data can also be stored in the system, if desired. If desired by a skilled person, these data can likewise be used by the control means for the purpose of controlling the heating means.

The parameters are preferably recorded in the database frequently, for instance every 10 seconds or, if desired, less or more often. In order to keep the amount of data limited it is possible to only register changes.

When the control means are moreover configured here to control the heating means and/or the belt pressure and/or the contact time before and/or during throughfeed of the material, a feed forward is achieved, whereby it is possible during the process to anticipate the influence of changes in one or more of the parameters which are stored in the database.

It has already been elucidated above that the outer periphery temperature, fluid temperature and the settings of the flow influencing means and/or heating means and/or the belt pressure and/or the contact time can be significant.

It will be briefly elucidated below how the further parameters could be used.

Recording data about the number of revolutions of the roller since the start of a calendering process makes it possible to determine the number of revolutions starting from which a good result can be obtained, and/or when the heating means can be switched off at the end of a calendering process. If desired, the device can comprise means for making it known that a calendering process can be started, for instance visually by means of lighting.

Properties of the material, for instance type of material and/or (specific) weight, usually expressed in gram/m², often determine a heat absorption by the material and thereby how the control means must control the heating means and/or the belt pressure and/or the contact time. Registering the power of the heating means in combination with registering the at least one property of the material can provide insight into this heat absorption, for instance by registering the amount of energy, i.e. power, required to keep the outer periphery of the roller at a determined temperature without throughfeed of a determined material, relative to the amount of energy required during throughfeed of a determined material. This information can be used to select a determined power for the heating means even before a determined material is actually fed through. The operator can enter which material will be fed through, for instance via an interface of the device. For a heavier material it is for instance possible to select a greater power than for a lighter material, since the heat absorption of a heavier material is usually higher than for a lighter material. This can be particularly advantageous when starting up a calendering process and when switching between different materials.

Properties of the transfer paper, for instance humidity and/or type of material and/or (specific) weight, usually expressed in gram/m², can determine a heat absorption by the transfer paper. By optionally also registering this, it is possible also to control on the basis hereof.

The ambient temperature can influence the energy loss of the roller. The heating means and/or the belt pressure and/or the contact time can therefore be controlled in desired manner on the basis of a measured ambient temperature, for instance by increasing a power of the heating means when the ambient temperature is lower than a determined value, and vice versa. An ambient temperature sensor can be provided for the purpose of measuring the ambient temperature.

The air humidity can likewise influence the energy consumption of the roller. An air humidity sensor can be provided for the purpose of measuring the air humidity.

Which calender is used can likewise influence a desired setting. This can comprise both the type of calender, and which calender is used from among calenders of the same type.

The power of drive means of the calender can likewise be of influence.

The belt of the calender can absorb heat. When the at least one property of the belt is known, it is for instance known how great the energy absorption of the belt in question can be, whereby the heating means can be controlled on the basis of these data in order to improve the process still further. Type of material and/or age of the belt can for instance be determining factors.

As elucidated above, it is possible to register the amount of energy, i.e. power, required to keep the outer periphery of the roller at a determined temperature without throughfeed of a determined material and with throughfeed of a determined material. This registered energy provides insight into how much energy leaks away without throughfeed of material, for instance due to heat absorption of the belt and/or due to radiation and/or due to a cold environment, and with throughfeed of material, due to heat absorption by the material. A more accurate process can be obtained by registering this energy by means of registering the power of the heating means and recording said parameters and controlling the heating means and/or the belt pressure and/or the contact time on the basis thereof.

In another embodiment of the device according to the invention the control means are configured to determine on the basis of at least periodically recorded settings of the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time of a plurality of prior calendering processes and on the basis of at least the at least one property of the same material how the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time must be set, and to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time in the determined manner.

A prior, successful process can be repeated by collecting said settings in the database, particularly for successful calendering processes, and optionally the other parameters as stated in claim 10, and by controlling the calender on the basis of these data.

In another embodiment of the device according to the invention the database and the control means are connected or at least connectable to each other, optionally wirelessly, for instance via a computer network, such as for instance the Internet.

In practical manner there is a connection between the database and the control means. This connection preferably takes place via a computer network. This has the advantage that the data as collected on the basis of a plurality of calenders according to the invention can be collected in one database. Because this one database contains all data relating to the operation of a plurality of calenders, even more data are available, which can result in a more reliable operation of the calender with a view to a good quality. Central processing of these data in one database moreover has the advantage that these data can be secured more easily and thereby more cheaply. Wireless connections are preferred here because they are very flexible and have sufficient bandwidth for the amount of data to be transferred.

It is possible for a connection between the database and the device to drop out at least temporarily. It can be advantageous for the control means to be configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of average values, more particularly on the basis of average values for a determined fed-through material, as soon as this happens.

The invention further relates to a set with a plurality of calenders according to one or more of the above described embodiments or with one or more of the above described features, wherein the control means of at least one of the calenders are configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time of that one calender on the basis of optionally periodically registered data of calendering processes performed with the calenders of the set.

It will generally be apparent to the skilled person that the advantages and/or elucidations described on the basis of the invention likewise apply to the set according to the invention.

It is advantageous here for optionally periodically registered data of calendering processes performed with a plurality of calenders of a set to be used in order to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time of a calender of the set. When a large number of calenders is used to collect data relating to the progression of the performed calendering processes, these data can serve as a basis for subsequent processes in order to increase the chances of a good quality of the print. This is because calendering processes are readily predictable the more parameters are known and/or are controlled. Periodically registering the data increases the amount of available data and enables a more accurate control.

Said one calender is preferably a calender of the set other than the calender of which the data are registered. In this way the progression of the process in one or more other calenders can be used to efficiently control this one calender.

The invention further relates to a method for controlling a calender according to any one of the foregoing claims, which method comprises the following steps, to be performed in any suitable order, of:

a) setting or determining a setting of the flow influencing means;

b) controlling the flow influencing means and thereby the flow of the fluid in the internal space by means of the control means so as to achieve the setting set or determined in step a), wherein a flow speed of the fluid can be set by the control in step b).

It will generally be apparent to the skilled person that the advantages and/or elucidations described on the basis of the device or set likewise apply to the method according to the invention.

Step a) can be performed by an operator who sets the control means in a suitable manner, for instance via an interface. Step a) is preferably performed by determining, for instance by means of the control means, a desired setting, for instance on the basis of a desired heat transfer between the fluid and the roller as elucidated above.

An additional step of further controlling the heating means and/or the belt pressure and/or the contact time can be provided.

When a calender according to at least claim 2 is controlled, it is preferred that a direction of the flow of the fluid is set by the control in step b) to a direction which is substantially opposite to a rotation direction of the roller.

An advantage hereof is elucidated above on the basis of claim 2.

When a calender according to at least claim 3 is controlled, it is preferred that a flow regime of the fluid can be varied between turbulent and laminar by the control in step b).

A turbulent flow contributes to a higher heat transfer between the fluid and the roller than a laminar flow, as is elucidated above.

During a start-up phase and/or shutdown phase of a calendering process the flow influencing means can be controlled by the control means such that the direction of the flow of the fluid is opposite to the rotation direction of the roller and/or the flow regime is turbulent.

A relatively high heat transfer between the fluid and the roller is hereby provided during the start-up phase and/or shutdown phase, whereby energy can be saved because printing can be started sooner or the heating means can be switched off sooner.

When a calender according to at least claim 5 is controlled, it is preferred that the first and second drive means are controlled separately of each other by the control means in step b).

An advantage hereof is elucidated above on the basis of claim 5.

When a calender according to at least claim 8 is controlled, it is preferred that the method further comprises the step c) of measuring the temperature of an outer periphery of the roller with the at least one first temperature sensor, and that the control means control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the outer periphery temperature measured in step c).

Because the temperature of the roller is here measured at a position close to the periphery of the roller, it is possible to better control the calendering process.

The method preferably comprises here the step d) of setting or determining a target temperature for the outer periphery of the roller, and wherein in step a) the desired setting is determined on the basis of the difference between the outer periphery temperature measured in step c) and the target temperature set in step d).

In this way it is possible to get the outer periphery temperature to a desired value in simple manner A desired value for the temperature (or target temperature) for the outer periphery is here set or determined at any given moment during step d). The flow influencing means, and preferably also the heating means and/or the belt pressure and/or the contact time, are also controlled on the basis of an outer periphery temperature measured in step c).

Setting the desired target temperature according to step d) can for instance take place before the control of the heating means by the control means as according to step b) has commenced. This provides the option of controlling the heating process during the method on the basis of the desired target temperature in order to achieve an efficient heating in this way. Performing step d) not until after or during or again after or during start-up of step b) can however also be preferred.

The value set or determined in step d) can here for instance be a value set by a human operator, but can however also originate directly from or at least be based on data from a different data source.

It is possible that during heating, heating takes place to roughly the desired target temperature. This means that a determined variation between the measured outer periphery temperature and the target temperature is disregarded or is permitted. This variation is preferably a maximum of 5° C., more preferably a maximum of 2° C., more preferably a maximum of 1° C.

When a calender according to at least claim 2 or 3 is controlled here, it is preferred that the flow influencing means are controlled by the control means in step b) such that the direction of the flow of the fluid is the direction opposite to the rotation direction of the roller and/or the flow regime is turbulent if the difference between the outer periphery temperature measured in step c) and the target temperature set or determined in step d) is greater than a determined value, and, optionally, that the flow regime is laminar or the speed of the flow is almost 0 m/s if the difference between the outer periphery temperature measured in step c) and the target temperature set or determined in step d) is smaller than a determined value.

At the moment that the difference between the measured outer periphery temperature and the target temperature is great it is advantageous to provide for turbulent flow and/or flow in the direction opposite to the rotation direction of the roller, since this increases the heat transfer. However, in order to prevent for instance an overshoot, it can be favourable to switch to a laminar flow and/or a substantially stationary fluid at the moment that the measured outer periphery temperature approaches the set or determined target temperature.

When a calender according to at least claim 9 is controlled, it is preferred that the method further comprises the step e) of measuring the temperature of the fluid with the at least one second temperature sensor, and wherein the control means control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the fluid temperature measured in step e).

Alternatively or optionally also measuring with a second temperature sensor will have the result that an even more precise control of the process can be realized.

When a calender according to at least claim 10 is controlled, it is preferred that the control means control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the data contained in the database.

As already described above in relation to the calender according to the invention, it is preferred in methods to have the control take place on the basis of at least one of the data stored in the database as described, since this makes the process more predictable and/or reproducible.

When a set according to the invention is controlled, it is preferred that the control means of said one calender control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of optionally periodically registered data from calendering processes performed with a plurality of calenders of the set.

In an embodiment at least one step of the method is performed iteratively.

Iteratively performing, i.e. repeating, at least one step has the result that the process is monitored more closely, which increases the reliability of the control by the control means. This can have a positive influence on the accuracy of a calendering process.

The invention will be further elucidated with reference to the accompanying figures, in which:

FIGS. 1A and 1B show schematically a calender according to a first embodiment of the invention, wherein FIG. 1A shows a vertical longitudinal section along the width of the calender and FIG. 1B shows a cross-section of the calender;

FIGS. 2A and 2B show schematically a calender according to a second embodiment of the invention, wherein FIG. 2A shows a vertical longitudinal section along the width of the calender and FIG. 2B shows a cross-section of the calender;

FIG. 3 show schematically the steps of a method according to a first embodiment of the invention.

The same elements are designated in the figures with the same reference numerals, increased by 100 for the second embodiment.

FIGS. 1A and 1B show a calender 1 according to a first embodiment of the invention. Calender 1 can be used for calendering processes, such as for instance transfer and/or fixation processes or laminating processes. Calender 1 comprises a rotatable roller 2, which roller is hollow and thereby defines an internal space 3 which in this case is filled with oil. Internal space 3 connects via a conduit 5 to an expansion tank 4 for the oil. Calender 1 comprises a drive shaft 6 for rotating driving of roller 2. Calender 1 further comprises a belt 7 co-acting with roller 2, which belt 7 is disposed via guide rollers 8 round a part of the periphery of roller 2, see FIG. 1B. For the sake of simplicity belt 7 is not shown in FIG. 1A. As is visible in FIG. 1B, a material 9 can be fed through between roller 2 and belt 7 for a determined contact time during a calendering process, wherein the contact time can particularly be the amount of time during which the material 9 is in direct or indirect contact with roller 2. The contact time can for instance depend on a rotation speed of roller 2. Disposed in this case in the internal space 3 of roller 2 are a plurality of heating elements 10, which heat the oil. Because the oil is heated, the oil can heat roller 2. A calendering process can particularly be controlled on the basis of at least one of the following three parameters, i.e. the degree of heating, which can for instance be set by setting a power of heating elements 10, a belt pressure, which can for instance be set by tightening belt 7 or arranging it more loosely, for instance using guide rollers 8, and the contact time, which can for instance be set by selecting a suitable rotation speed, i.e. number of revolutions, of roller 2. Calender 1 comprises for this purpose one or more control means, for instance in the form of a processor (not shown).

Several aspects of the invention will be elaborated further hereinbelow. The aspects can be provided alone or in combination. The elements of calender 1 further described in the context of the aspects can each be provided alone or in combination.

According to an aspect of the invention, calender 1 comprises in this first exemplary embodiment flow influencing means for initiating and/or influencing a flow of the oil in internal space 3. In this case the flow influencing means comprise a rotor 20 which is disposed in roller 2 and is rotatably drivable by a drive shaft 21. In this example rotor 20 comprises a plurality of blades 22, using which the oil can be set into motion. In this example rotor 20 comprises a cylindrical body, wherein the blades 22 extend outward from the cylindrical body, substantially in the direction of roller 2. The oil is situated between rotor 20 and roller 2. The drive shaft 6 for rotating driving of roller 2 and the drive shaft 21 for rotating driving of rotor 20 are configured to drive roller 2 and rotor 20 separately of each other. Rotor 20 can particularly be driven in a rotation direction 23, which rotation direction 23 is opposite to a rotation direction 24 of roller 2, see FIG. 1B. The flow direction of the oil can hereby be set to a direction opposite to roller 2. The rotation speed of rotor 20 can be set between 0 revolutions/s, i.e. the rotor does not rotate, and a maximum rotation speed V_(rotor,max), for instance expressed in revolutions/s or revolutions/min. A flow speed of the oil can hereby be set, particularly between a substantially stationary flow and a maximum flow speed V_(max). By selecting a suitable rotation speed for rotor 20 the flow of the oil can be laminar, i.e. for 0≤V_(rotor)≤V_(rotor,laminar), or turbulent, i.e. for V_(rotor, laminar)<V_(rotor)≤V_(rotor,max). By selecting a suitable speed of the oil and/or the flow regime of the oil a heat transfer from the oil to roller 2 can be set, and particularly reduced or increased. The rotor can be controlled by the stated or further control means.

According to another aspect of the invention, in this first exemplary embodiment calender 1 comprises at least one temperature sensor 30 for measuring the temperature of an outer periphery of roller 2. Temperature sensor 30 is disposed in an area of roller 2 where the material 9 will come into contact with the roller, but at a position where material 9 is guided away from roller 2, see FIG. 1B. Temperature sensor 30 hereby measures the outer periphery temperature at a location relevant to the process, but without influencing the calendering process. FIGS. 1A and 1B show one first temperature sensor 30 but, if desired, a plurality of first temperature sensors 30 can be provided, these being disposed distributed over the width b of roller 2 for the purpose of measuring the temperature of an outer periphery of roller 2 distributed over the width b of roller 2. First temperature sensor 30 is shown schematically in FIGS. 1A and 1B as being arranged on the outer periphery of roller 2. Such a sensor 30 can for instance comprise a thermocouple. Alternatively, it is also possible to dispose the sensor at a distance from roller 2, for instance by using an infrared sensor. In this first embodiment of calender 1 the calender further comprises a second temperature sensor 31 for measuring the temperature of the oil. If desired, a plurality of second temperature sensors 31 can be provided, these being disposed distributed over the width b roller 2 for the purpose of measuring the oil temperature distributed over the width b of roller 2. Such a sensor 31 can for instance comprise a thermocouple. Said control means can be configured to control the heating means and/or the belt pressure and/or the contact time on the basis of the measured outer periphery temperature and optionally the measured oil temperature.

According to another aspect of the invention, calender 1 or a system of which the calender forms part comprises a database 40 which is wirelessly connected to calender 1 in this example. Data can be stored in database 40, wherein said control means can further be configured to control the rotor 20 and/or the heating elements 10 and/or the belt pressure and/or the contact time on the basis of at least one of the data contained in database 40. At least one of the following data can for instance, though not exclusively, be stored, optionally periodically, in database 40:

-   -   the measured outer periphery temperature of roller 2;     -   the measured fluid temperature;     -   the contact time;     -   the belt pressure;     -   a power of heating elements 10;     -   number of revolutions of roller 2 since the start of a         calendering process;     -   at least one property of the at least one material 9 being fed         through calender 1;     -   at least one property of a transfer paper optionally being fed         through the calender;     -   an ambient temperature;     -   an air humidity;     -   which calender is used;     -   a power of drive means of the calender;     -   at least one property of the belt 7 of the calender.

If desired, database 40 can also store data of other calenders 1. In this way the calender can be controlled even more accurately.

FIGS. 2A and 2B show a calender 101 according to a second embodiment of the invention. Only the differences with the calender 1 according to the first embodiment of FIGS. 1A and 1B will be described here. For a further description of calender 101 reference is made to the figure description associated with FIGS. 1A and 1B.

Calender 101 comprises a rotatable roller 102, which roller is hollow and thereby defines an internal space 103, which in this case is filled with air. In this embodiment roller 102 forms a closed system for the air. Disposed in this case in the internal space 103 of roller 102 are a plurality of heating elements 110 which both heat the air and also directly heat roller 102 by means of radiation.

In this second embodiment the flow influencing means for influencing the flow of, in this case, the air comprise two air conduits 125 with a number of openings 128 via which air can flow into the internal space 103 of roller 102. Openings 128 are formed and/or provided with orienting means such that the air flows into space 103 in a direction 123 which is opposite to the rotation direction 124 of roller 102. Air conduits 125 extend through roller 102 and are connected via an outer side of roller 102 to, in this case, two air discharge conduits 126. Air discharge conduits 126 comprise openings 129 for drawing in air. The air extracted via the air discharge conduits 126 can be supplied to roller 102 again via air conduits 125. A pump 127 is provided for the purpose of extracting and blowing in the air. Pump 127 can be set between a minimum power of 0, wherein no extraction and blowing in of the air takes place and wherein the air is substantially still, and a maximum power V_(pump,max) whereby a maximum flow speed of the air is brought about. By selecting a suitable power for pump 127 the flow of the air can be laminar, i.e. for 0≤V_(pump)<V_(pump,laminar), or turbulent, i.e. for V_(pump,laminar)<V_(pump)≤V_(pump,max). By selecting a suitable speed of the air and/or the flow regime of the air a heat transfer from the air to roller 102 can be set, and particularly reduced or increased. The pump 127 can be controlled by the stated or further control means.

Said temperature sensors 130 and/or 131 can if desired also be provided in this second embodiment.

Said database 140 can if desired also be provided in this second embodiment.

FIG. 3 shows the steps of a first embodiment of the method according to the invention.

Step 50 comprises of setting or determining a setting of the flow influencing means. Step 51 comprises of measuring the outer periphery temperature of the roller. Step 52 comprises of measuring the fluid temperature. Step 53 comprises of setting or determining a target temperature for the outer periphery of the roller. Step 54 comprises of making data from a stated or other database available. Step 55 comprises of controlling the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time for the purpose of controlling a calendering process on the basis of at least one of the settings of the flow influencing means set or determined in step 50, outer periphery temperature measured in step 51, fluid temperature measured in step 52, target temperature set or determined in step 53, and data from the database made available in step 54.

Although the invention is elucidated above on the basis of a number of specific examples and embodiments, the invention is not limited thereto. The invention instead also covers the subject matter defined by the following claims. 

1-25. (canceled)
 26. A calender, comprising: a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set.
 27. The calender according to claim 26, wherein the control means are configured to control the flow influencing means such that a direction of the flow of the fluid is substantially opposite to a rotation direction of the roller.
 28. The calender according to claim 26, wherein the control means are configured to control the flow influencing means such that the flow regime of the fluid is variable between turbulent and laminar.
 29. The calender according to claim 26, wherein the flow influencing means comprise a rotatable rotor with a number of blades which are disposed in the roller, and further wherein: the calender comprises first drive means for rotatably driving the roller and second drive means for rotatably driving the rotor, wherein the control means are configured to control the first and second drive means separately of each other; and/or the rotor comprises a cylindrical body disposed in the internal space of the roller, wherein the fluid is situated between the rotor and the roller, at least during use of the calender, wherein the blades extend outward from the cylindrical body, substantially in the direction of the roller.
 30. The calender according to claim 26, wherein the flow influencing means comprise at least one fluid conduit extending into the internal space and having at least one opening for supplying fluid from the at least one fluid conduit via the at least one opening to the internal space of the roller, and comprising at least one fluid discharge for discharging fluid from the internal space.
 31. The calender according to claim 26, further comprising: at least one first temperature sensor for measuring the temperature of an outer periphery of the roller, wherein the control means are configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the measured outer periphery temperature; and at least one second temperature sensor for measuring the temperature of the fluid, wherein the control means are further configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the measured fluid temperature.
 32. The calender according to claim 26, comprising a database in which at least one of the following data is stored: a measured outer periphery temperature of the roller; a or the measured fluid temperature; the contact time; the belt pressure; a power of the heating means; number of revolutions of the roller since the start of a calendering process; at least one property of the at least one material being fed through the calender; at least one property of a transfer paper being fed through the calender; an ambient temperature; an air humidity; which calender is used; a power of drive means of the calender; and at least one property of a belt of the calender, and wherein the control means are further configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of at least one of the data contained in the database.
 33. The calender according to claim 32, wherein the control means are configured to determine on the basis of at least periodically recorded settings of the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time of a plurality of prior calendering processes and on the basis of at least the at least one property of the same material how the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time must be set, and to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time in the determined manner; and wherein the database and the control means are connectable to each other wirelessly or via a computer network.
 34. A set with a plurality of calenders according to claim 26, wherein the control means of at least one of the calenders are configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time of that one calender on the basis of periodically registered data of calendering processes performed with the calenders of the set.
 35. A method for controlling a calender according to claim 26, which method comprises the following steps: a) setting or determining a setting of the flow influencing means; and b) controlling the flow influencing means and thereby the flow of the fluid in the internal space by means of the control means so as to achieve the setting set or determined in step a), wherein a flow speed of the fluid is settable by the control in step b).
 36. The method according to claim 35, comprising controlling a calender comprising: a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set, wherein the control means are configured to control the flow influencing means such that a direction of the flow of the fluid is substantially opposite to a rotation direction of the roller; and wherein a direction of the flow of the fluid is set by the control in step b) to a direction which is substantially opposite to a rotation direction of the roller.
 37. The method according to claim 35, comprising controlling a calender comprising: a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set; wherein the control means are configured to control the flow influencing means such that the flow regime of the fluid can vary between turbulent and laminar; and wherein a flow regime of the fluid can be varied between turbulent and laminar by the control in step b).
 38. The method according to claim 36, wherein during a start-up phase and/or shutdown phase of a calendering process the flow influencing means are controlled by the control means in step b) such that the direction of the flow of the fluid is the first direction and/or the flow regime is turbulent.
 39. The method according to claim 35, comprising controlling a calender comprising: a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set; wherein the flow influencing means comprise a rotatable rotor with a number of blades which is disposed in the roller, and further wherein: the calender comprises first drive means for rotatably driving the roller and second drive means for rotatably driving the rotor, wherein the control means are configured to control the first and second drive means separately of each other; and/or the rotor comprises a cylindrical body disposed in the internal space of the roller, wherein the fluid is situated between the rotor and the roller, at least during use of the calender, wherein the blades extend outward from the cylindrical body, substantially in the direction of the roller; and wherein the first and second drive means are controlled separately of each other by the control means in step b).
 40. The method according to claim 35, comprising controlling a calender comprising: a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set; at least one first temperature sensor for measuring the temperature of an outer periphery of the roller, wherein the control means are configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the measured outer periphery temperature; and at least one second temperature sensor for measuring the temperature of the fluid, wherein the control means are further configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the measured fluid temperature; which method further comprises the step c) of measuring the temperature of an outer periphery of the roller with the at least one first temperature sensor, and the control means control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the outer periphery temperature measured in step c).
 41. The method according to claim 40, further comprising the step d) of setting or determining a target temperature for the outer periphery of the roller, and wherein in step a) the desired setting is determined on the basis of the difference between the outer periphery temperature measured in step c) and the target temperature set in step d); and controlling a calender comprising: a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set; wherein the control means are configured to control the flow influencing means such that a direction of the flow of the fluid is substantially opposite to a rotation direction of the roller; and wherein the flow influencing means are controlled by the control means in step b) such that the direction of the flow of the fluid is the direction opposite to the rotation direction of the roller and/or the flow regime is turbulent if the difference between the outer periphery temperature measured in step c) and the target temperature set or determined in step d) is greater than a determined value, and, that the flow regime is laminar or the speed of the flow is almost 0 m/s if the difference between the outer periphery temperature measured in step c) and the target temperature set or determined in step d) is smaller than a determined value.
 42. The method according to claim 35, comprising controlling a calendar comprising:— a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set; at least one first temperature sensor for measuring the temperature of an outer periphery of the roller, wherein the control means are configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the measured outer periphery temperature; and at least one second temperature sensor for measuring the temperature of the fluid, wherein the control means are further configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the measured fluid temperature; which method further comprises the step e) of measuring the temperature of the fluid with the at least one second temperature sensor, and wherein the control means control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the fluid temperature measured in step e).
 43. The method according to claim 35, comprising controlling a calendar comprising: a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set; the calender further comprising a database in which at least one of the following data is stored: a measured outer periphery temperature of the roller; a or the measured fluid temperature; the contact time; the belt pressure; a power of the heating means; number of revolutions of the roller since the start of a calendering process; at least one property of the at least one material being fed through the calender; at least one property of a transfer paper being fed through the calender; an ambient temperature; an air humidity; which calender is used; a power of drive means of the calender; and at least one property of a belt of the calender, wherein the control means are further configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of at least one of the data contained in the database; and wherein the control means control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of the data contained in the database.
 44. The method according to claim 35, comprising controlling a calendar comprising: a rotatable roller, which roller is hollow and thereby defines an internal space which is configured to be filled at least partially with a heatable fluid; a belt, co-acting with the roller, with a determined belt pressure, wherein at least one material for feeding through the calender is situated between the roller and the belt for a determined contact time during throughfeed through the calender; heating means for heating the fluid, which heating means are disposed in the internal space; and one or more control means for controlling the heating means and/or the belt pressure and/or the contact time, wherein the calender comprises flow influencing means for initiating and/or influencing a flow of the fluid in the internal space, wherein a further control means are configured to control the flow influencing means and thereby the flow of the fluid in the internal space in freely settable manner, such that a flow speed of the fluid can be set; wherein the control means of at least one of the calenders are configured to control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time of that one calender on the basis of periodically registered data of calendering processes performed with the calenders of the set; and wherein the control means of said one calender control the flow influencing means and/or the heating means and/or the belt pressure and/or the contact time on the basis of periodically registered data from calendering processes performed with a plurality of calenders of the set.
 45. The method according to claim 35, wherein at least one step of the method is performed iteratively. 